1. Field of the Invention
The present invention relates to a network management system and a switch in such a case that a plurality of communications networks managed by different companies (common carriers) are so constructed as to be geometrically dispersed, more particularly, relates to a network management system and a switch capable of moving an user terminal among areas covered by the plurality of communication networks and capable of using the user terminal before and after the movement.
2. Related Background Art
In a mobile telephone business dealing with, e.g., a portable telephone and an automobile telephone, there is a case in that a communications network is constructed by an each company (a common carrier) in each area and a telephone service is provided. Such a geometrical division of the communications networks will be, it can be considered, increasingly promoted from now on into the future in terms of a world-wide trend of privatizing the telephone businesses and a request from the Antimonopoly Law.
If the common carrier of the communications network thus differs per area, however, a terminal making a subscription contact with a specific common carrier and allocated with a telephone number is in principle permitted to use the telephone number only in the area within a coverage of the communications network managed by the common carrier concerned. Therefore, the user, when requesting the use of the terminal in an area different from the area within the coverage of the above communications network, must make the subscription contact once again with a common carrier of the communications network covering this different area. As a result, this carrier allocates a new telephone number which is absolutely different from the telephone number used so far. This is attributed to the fact that the telephone number partially contains a unique number (switch identification number=telephone exchange number) per switch (another part of the telephone number excluding the telephone exchange number corresponds to a subscriber number unique to the terminal).
A way known as "roaming" in, e.g., the mobile telephone business has been generalized in order to obviate both troublesomeness in making the subscription contract with each common carrier and inconvenience for changing the telephone number. This way is that when the terminal of a subscriber (herein referred to as a subscriber "B") who makes a subscription contract with one common carrier (herein called a common carrier "X") and is thereby allocated with a telephone number (e.g., "25713514", "2571" of which is a telephone exchange number of a local switch of the common carrier "X") moves to an area within a coverage by the communications network of other common carrier (herein referred to as a common carrier "Y"), this terminal is provided automatically or manually with a network number (e.g., "28371553") defined as a telephone number effective in the communications network of the common carrier "Y". Further, when a call setting request occurs upon dialing the original telephone number "25713514", a call setting process with respect to the terminal of the subscriber "B" is executed by automatically converting the telephone number "25713514". In this call setting request into the network number "28371553" and automatically transferring this network number to the switch of the common carrier "Y".
With this system, it might be simply enough for a subscriber (herein called a subscriber "A") telephoning the subscriber "B" to recognize the original telephone number, and the subscriber "B" himself or herself has no necessity for knowing the network number. Thus, the apparent telephone number is invariable, and hence this telephone number may also be referred to as a "portable number". Further, a function of making the apparent telephone number invariable in this way may also be termed a "number portability function".
FIG. 15 is a schematic explanatory diagram showing a case where such a number portability function is actualized in an intelligent network. As illustrated in FIG. 15, when the subscriber "A" dials a telephone number "25713514" (step 71), a call setting request containing this telephone number "25713514" is transferred to a local switch 101 of the common carrier "X" from a local switch 100 of a switching network accepting the terminal of the subscriber A (step 72). This local switch 101 judges that the terminal "B" of the subscriber "B" does not exist in an area within a coverage by a communications network of the carrier "X", and transfers this call setting request, after adding a dedicated access code thereto, to an SSP (Service Switching Point, a higher-order switch than local switches of each common carrier) 102 (step 73). Thereupon, this SSP 102 transfers the call setting request to an SCP (Service Control Point) 103 on the basis of the access code (step 74).
A database of this SCP 103 is prepared with a correspondence table showing telephone numbers (portable numbers) and network numbers, and hence the SCP 103, after automatically converting the telephone number "25713514" in the call setting request into a network number "28371553" (step 75), transfers this call setting request to a local switch 104 of the common carrier "Y" via the SSP 102 (step 76).
The network number "28371553" allocated to the subscriber "B" is registered in the local switch 104 at the point of time when the terminal of the subscriber "B" moves, and it is therefore feasible to execute a process for establishing a call between this terminal and the terminal of the subscriber "A" by calling the terminal of the subscriber B based on the network number "28371553".
Further, FIG. 16 is a schematic explanatory diagram in the case where the number portability function is carried out by the switch itself. As in the case of FIG. 16, when the call setting request containing the telephone number "25713514" is transferred (S81, S82), the local switch 105 of the common carrier "X" judges that the terminal of the subscriber "B" does not exist in the area within the coverage by the common carrier "X". Since the switch 105 is prepared with the correspondence table showing the telephone numbers (portable numbers) and the network numbers, the call setting request is, after the telephone number "25713514" in the call setting request has been automatically converted into the network number "28371553" (step 83), transferred to the local switch 104 of the common carrier "Y" by use of a call forwarding function (step 84). The local switch 104 having received this call setting request is, as the case of FIG. 16, capable of executing the process for establishing the call between the terminal of the subscriber "B" and the terminal of the subscriber "A".
Now, in the ordinary dial telephone, only the numerals of 0-9 can be transmitted as dial signals to the switch. Further, in a push-phone, only the numerals of 0-9 and signals * and # can be transmitted as the dial signals. The signals * and # are used only within the switch to which the telephone is connected. Note that the processing is carried out based on the hexadecimal numbers (1-9 and A-F; i.e., a single character is expressed by a 4-bit binary value) within the switch.
Therefore, the prior art switch, when receiving the call setting request, as shown in FIG. 17, analyzes the numerals of the telephone number contained in the same request (after being converted based on the hexadecimal number) (S91) and, if the numerals are composed of only some of 1-9 and A (corresponding to "0" of a dial signal and a push signal), continues the processing. If numerals excluding 1-9 and A are contained, the switch judges that the received numerals are wrong, and finishes the processing (S92).
As a result, when actualizing the number portability function by use of the prior art switch, as the case of the ordinary telephone number, only the numerals of 1-9 and "A" can be used as the network number.
As described above, only ten kinds of numerals can be used both for the ordinary telephone number and network number, and hence there are only 10.sup.4 ways of permutation of the registrable subscriber numbers. Accordingly, the number of telephone numbers allocatable to the subscribers having made the subscription contracts with the common carrier "Y" becomes smaller as a larger number of network numbers are registered in the switch 104 of the common carrier "Y". For instance, in the examples shown in FIGS. 15 and 16, "28371553" allocated as the network number can not be allocated as a telephone number of other subscriber. Consequently, there arises a problem in which the apparent subscriber capacity decreases.